Answer to your question, neither.

According to the old histories and religious writings, the first person who could have been called Jewish - Abraham - wasn't and wouldn't have any idea of what the term meant.

Next clarification is the odd perception among westerners - esp Christians - that the entire OT is the product of the Jewish religion. Well it wasn't and isn't.

For one thing, the story of Noah predates Abraham and is shared - also claimed - by many different cultures including the Arabs. Nor is there any reason to suppose that Abraham's tale is completely original either. Compare NT stories with the old pagan religions of Rome. See Mythracism myths V NT Messiah.

All in all, one can agree with Rebbi-Sol above if the entire population of Ur ceased to exist, after Abraham left the city - now near Bagdad in modern Iraq.

But it didn't. So there is one heckuva gap in history right there.

Modern Jewish people are as descended from Urians as modern day Urians and if they did not have different religions it would be hard to distinguish the one from the other.